Three-dimensional (3D) television has been a technology trend in recent years that is targeted to bring viewers sensational viewing experience. Multi-view video is a technique to capture and render 3D video. The multi-view video is typically created by capturing a scene using multiple cameras simultaneously, where the multiple cameras are properly located so that each camera captures the scene from one viewpoint. The multi-view video with a large number of video sequences associated with the views represents a massive amount data. Accordingly, the multi-view video will require a large storage space to store and/or a high bandwidth to transmit. Therefore, multi-view video coding techniques have been developed in the field to reduce the required storage space and the transmission bandwidth. In three-dimensional and multi-view coding systems, the texture data as well as depth data are coded.
Currently, extensions of HEVC (High Efficiency Video Coding) are being developed, including range extensions (RExt) and 3D extensions. The range extension targets at non-4:2:0 color formats, such as 4:2:2 and 4:4:4, and video data with higher bit-depths such as 12, 14 and 16 bit-per-sample while the 3D extension targets at the coding of multi-view video with depth data.
One of the most likely applications utilizing RExt is screen sharing over wired-connection or wireless. Due to specific characteristics of screen-content, coding tools have been developed that demonstrated significant gains in coding efficiency. Among them, the palette coding (a.k.a. major color based coding) techniques represent block of pixels using indices to the palette (major colors), and encode the palette and the indices by exploiting spatial redundancy as disclosed in JCTVC-P0249 (Sun et al., “Non-RCE4: A combination of the four-neighbor major color index prediction in JCTVC-P0098 and a simplified transition copy mode from JCTVC-P0115 on top of RCE4 Test1”, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 16th Meeting: San José, US, 9-17 Jan. 2014, Document: JCTVC-P0249).
In order to support the auto-stereoscopic multi-view display more practically, multi-view video plus depth (MVD) format was introduced as a new 3D video format as disclosed in JCT3C-G1005 (Zhang et al, Test Model 7 of 3D-HEVC and MV-HEVC, Joint Collaborative Team on 3D Video Coding Extensions of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG, 7th Meeting: San José, US, 11-17 Jan. 2014, Document: JCT3V-G1005). The MVD format consists of a texture image and its associated depth map. Unlike a texture image representing the luminance and chrominance information of an object, a depth map presents the distance between an object and a camera as a gray scale image. The depth map is generally employed for virtual view rendering as non-visual information. Since the MVD format enables the 3D display to generate virtual texture images for arbitrary views by using the depth image based rendering (DIBR) technique, only a small number of views need to be transmitted. Due to these advantages, the MVD format is being widely used as a codec input for the 3D video coding.
Due to the signal characteristics of the depth map or screen contents, it is desirable to develop coding techniques to take advantage of the nature of smooth areas in the depth map or screen contents to further improve the coding efficiency.